Future Changes in Oceanography and Biogeochemistry Along the Canadian Pacific Continental Margin

Abstract

Model projections of ocean circulation and biogeochemistry are used to investigate large scale climate changes under moderate mitigation (RCP 4.5) and high emissions (RCP 8.5) scenarios along the continental shelf of the Canadian Pacific Coast. To reduce computational cost, an approach for dynamical downscaling of climate projections was developed that uses atmospheric climatologies with augmented winds to simulate historical (1986–2005) and future (2046–2065) periods separately. The two simulations differ in initial and lateral open boundary conditions. For each simulation, the daily climatology of surface winds in the driving model was augmented with high-frequency variability from an atmospheric reanalysis product. The “time-slice” approach was able to reproduce the observed climate state for the historical period. Sensitivity tests confirmed that the high frequency wind variability plays an essential role in freshwater distribution in this region. Projections suggest that sea surface temperature will increase by 1.8–2.4°C and surface salinity will decrease between −0.08 and −0.23 depending on whether a moderate or high emissions scenario is used. Stratification increases throughout the region and there is some evidence of nutrient limitation near the surface. Primary production and phytoplankton productivity (chlorophyll) also increase. Density surfaces are relocated deeper in the water column and this change is mainly driven by surface heating and freshening. Changes in saturation state are mainly due to anthropogenic CO2 with minor contributions from solubility, remineralization and advection. There is little difference between RCP 4.5 and RCP 8.5 with regard to projections of deoxygenation and acidification. The depths of the aragonite saturation state and the oxygen minimum zone are projected to become shallower by ≃ 100 and ≃ 75 m respectively. Extreme states of temperature, oxygen and acidification are projected to become more frequent and more extreme, with the frequency of occurrence of [O2]<60 mmolm-3 expected to approximately double under either scenario.

Marine CO<sub>2</sub> system variability along the northeast Pacific Inside Passage determined from an Alaskan ferry

“…Resolving environmental variability, even to the point of capturing seasonal cycles, remains a challenge in many settings due to a lack of measurements (Hales et al, 2008). In the northeast Pacific between British Columbia (BC) and southeast Alaska (AK), modeling efforts have aided in addressing this knowledge gap and have indicated the relative signifi-cance of freshwater input (Siedlecki et al, 2017;Hauri et al, 2020) and its source character (Pilcher et al, 2016), as well as projected warming, deoxygenation, and acidification on multidecadal timescales (Holdsworth et al, 2021). However, observations remain essential to evaluate model output and confirm our understanding of the governing processes that shape marine CO 2 system variability, particularly in nearshore settings.…”

Ocean biogeochemistry in the Canadian Earth System Model version 5.0.3: CanESM5 and CanESM5-CanOE

“…However, for the reasons discussed above, a prognostic Fe cycle with a fixed phytoplankton Fe/N remains problematic, and the model would still have a single detritus sinking speed and remineralization length scale. We are also developing CanOE for regional downscaling applications (Hayashida, 2018;Holdsworth et al, 2021), and it is likely that the simplification of having a single particle sinking speed is not well suited to a domain with complex topography and prominent continental shelf and slope. The number of tracers in CanOE is not particularly large compared with other CMIP6 models.…”

“…The NEMO system is a publicly available archive of codes based on the OPA (Océan PArallelisé) ocean model (Madec and Imbard, 1996;Guilyardi and Madec, 1997). It comes with two options for biogeochemistry: PISCES (Pelagic Interactions Scheme for Carbon and but have also been implemented in NEMO 3.6 for regional downscaling applications (Holdsworth et al, 2021).…”

Comment on bg-2021-266

“…Resolving environmental variability, even to the point of capturing seasonal cycles, remains a challenge in many settings due to a lack of measurements (Hales et al, 2008). In the Northeast Pacific between British Columbia (BC) and southeast Alaska (AK), modelling efforts have aided in addressing this knowledge gap, and have indicated the relative significance of freshwater input (Siedlecki et al, 2017;Hauri et al, 2020) and its source character (Pilcher et al, 2016), as well as projected warming, deoxygenation, and acidification on multi-decadal time scales (Holdsworth et al, 2021). However, observations at appropriate time and space scales remain essential to evaluate model output and confirm our understanding of the governing processes that shape the variability, particularly in nearshore settings that are typically not well parameterized.…”